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bambuntu
Asked: 2012-03-01 17:29:13 +0800 CST

Automate Password Set And Verify

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I'm using this to set passwords in a script:

usermod -p `mkpasswd -H md5 passwordText` user

I need to create an exception in my script, just in case this command fails. What file contains the encrypted password and how do I reverse the encryption so I can verify it was written to the file correctly?

Edit: I finally found the problem with the line above. The password was allowing symbols that were being interpreted as wildcards on the command line making it appear as if the command itself failed. Nonetheless, it's lead me to new things I'm glad I know now.

encryption automation password

2 Answers

  1. Best Answer

    Instead of reversing the the shadow- file, why not just do:

    usermod -p `mkpasswd -H md5 passwordText` user

if [ $? -ne 0 ]; then
    echo "Changing password failed!!!!!!"
fi

    You could replace whatever you want in the if block, but if a command ever fails for usermod it'll return a non-zero status.

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  2. The password is stored in /etc/shadow and you can try to confirm it with john the ripper.

    I am not sure if posting tutorials for john are allowed here, if so I can write one easily enough, but if not a google search will show you how.

    Last I looked, John needed a patch, but the bug report on launchpad seemed to indicate that the patch was incorporated into the repos, so I would try the un-patched version first (I know, lazy =) ).

    Short of john, su - test_user -> enter password.

    Brief tutorial on john the ripper:

    Install john

    sudo apt-get install john

    Prepare the working database (I made a user "test" with a weak password for this example).

    sudo unshadow /etc/passwd /etc/shadow > password.db

    Run john

    john password.db

Loaded 2 password hashes with 2 different salts (generic crypt(3) [?/64])
Remaining 1 password hash
guesses: 0  time: 0:00:00:03 0% (2)  c/s: 222  trying: monday - emily

    As you can see, john cracked the weak password in 0.03 seconds, my user password is too strong for john so I aborted it with Crtl + c

    Show the password

    john --show password.db

test:testing:1001:1001:,,,:/home/test:/bin/bash

1 password hash cracked, 1 left

    Here we see the user "test" with the password "testing"

    su test
Password:

    test@ufbt:/home/test

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